This invention relates to a method for installing a ducting system with branches, wherein at a point where a branch is desired, a tubular branch element with an inlet opening, an outlet opening and at least one branch opening is arranged between two opposite free ends of a continuous duct of the system, with the distance between the opposite free ends of the duct being less than the distance between the inlet and the outlet opening of the branch element.
Such a method is known from GB-A-2,267,183.
Currently, the part of telecommunications networks that extends from exchanges, for instance exchanges for telephony or for community antenna installations, to the houses or buildings of users, still consists largely of copper cable. The networks mutually connecting the exchanges by contrast already largely consist of fiber optic cable. The network consisting of copper cable has a telescopic structure, with the cables consisting of a very large number of twisted pairs, and with welded joints between a main cable and a branch cable, the main cable having a greater number of twisted pairs than does a branch cable. In the future, it will be desired to install fiber optic cable instead of copper cable in the lines to the users as well, in view of the greatly superior properties of fiber optic cable as compared with copper cable. When using fiber optic cables, however, it is not desirable to have a large number of joints in view of the high costs per joint and the relatively substantial damping caused by a joint in proportion to the total signal damping of a fiber optic cable.
The article "Subducts: The answer to Honolulu's growing pains" by Herman S. L. Hu and Ronald T. Miyahira in Telephony, Apr. 7, 1980, pages 23-35, describes a proposal to accommodate fiber optic cables in a separate guide tube or subduct, with four guide tubes installed in a primary duct forming part of a primary duct network. By using the guide tubes, it is possible, as the need for telecommunications connections increases, to provide a fiber optic cable in more of the guide tubes, without this fiber optic cable being hampered during installation by cables already present. At branches, a joint is made in the fiber optic cable.
Further, EP-A-0,108,590 describes a ducting network, the ducts of which have priorly been provided with a number of separate channels, allowing a separate fiber optic cable to be installed in each channel without armour or water barrier. The duct provided with channels protects the fiber optic cables against external influences, such as moisture and the like. In this way, as it were, a network with individual cables to each house is created, with the cables being arranged in parallel channels up to the branches. The existing ducts with preformed channels, even if they are provided with a water barrier, are not suitable to be buried directly in the ground. A mechanical protection is necessary. In the art, for that purpose, use is made of an existing infrastructure of concrete pipes of large dimensions. At every point where a duct with channels is coupled to another duct with channels, this necessitates the use of relatively costly junction boxes. In such a junction box each of the continuous channels is connected with the corresponding channel of a next duct by means of a coupling element and any channels to be branched off are likewise connected with channels in a branch duct by means of coupling elements. In the channels coupled in such a manner, the fiber optic cables can be installed without a joint from the main duct to the branch duct.